During the last decades there has been a substantial global increase in the amount of carbon dioxide emission to the atmosphere. Emissions of carbon dioxide into the atmosphere are thought to be harmful due to its “greenhouse gas” property, contributing to global warming. Following the Kyoto agreement, carbon dioxide emission has to be reduced in order to prevent or counteract unwanted changes in climate. Large anthropogenic sources of carbon dioxide emission are processes that combust fossil fuels, for example coal, natural gas or petroleum products, for electricity generation, transportation and heating purposes, and for production of steel and cement. These processes result in the production of gases comprising carbon dioxide. Thus, removal of at least a part of the carbon dioxide prior to emission of these gases into the atmosphere is desirable.
Processes for removal of carbon dioxide from gases are known in the art. Many processes are based on liquid absorption processes, with varying compositions of the absorption liquids. A drawback of these processes is the high energy consumption in the stripper unit to recover the absorbent, leading to a lower overall energy output.
Other processes make use of solid adsorbents.
The effect of moisture on the CO2 uptake of several adsorbents is discussed in “Flue gas treatment via CO2 absorption”, A. Sayari et al., Chem. Eng. J. 171 (2011) 760-774, for systems for which studies in the literature were available. Sayari indicates that moisture adversely affects CO2 uptake in zeolites and activated carbon, and that moisture adversely affects the stability and CO2 uptake of metal organic frameworks (MOFs) and zeolite-like MOFs (ZMOFs). Covalent organic frameworks (COFs) do not have hydrophilic adsorption sites, but showed a low CO2 uptake. Sayari further reports that moisture enhanced the CO2 capacity of polyethylene-imine (PEI) impregnated MCM-41 silica. Mono-ethanolamine improved the moisture tolerance of 13X zeolite. Sayari indicates that PEI impregnated silicon dioxide (CARiACT) and PEI impregnated MPPA (Diaion) showed enhanced adsorption capacity due to moisture.
EP-A-2463013 describes a process for removing carbon dioxide from a gas stream in an energy-efficient and relatively simple manner by contacting the gas stream with a regenerable solid adsorbent in a circulating fluidized bed system with two reactors, each having a single stage fluidized bed. The disadvantage of this process is that high CO2 capture efficiencies (percentage of CO2 removed from the gas) require high solid recirculation rates and/or high flows of stripping gas into the regenerator and thus high amounts of regeneration energy.
There is a need for a more efficient process for the removal of carbon dioxide from gases using solid adsorbents.